This invention relates in general to microvalves of the general type described and illustrated in U.S. Pat. Nos. 7,210,502, 7,803,281, 8,011,388, 8,113,482, and 8,156,962 and in U.S. Published Patent Application Nos. 2007/0172362, 2007/0251586, 2008/0042084, 2009/0123300, 2010/0012195, 2010/0084031, 2011/0127455, 2012/0000550, 2012/0145252, 2012/0140416, 2012/0295371, and 2012/0299129. The disclosures of all of these patents and patent applications are incorporated herein by reference.
In particular, this invention relates to an improved system for a microvalve that is provided with an integrated capability of sensing the flow of fluid therethrough for controlling the operation of the microvalve in response thereto.
A typical refrigerant cooling system for a device to be cooled includes a source, such as a compressor, that selectively provides a fluid, such as a liquid refrigerant, to a consuming device, such as an evaporator coil. To accomplish this, the source communicates through a temperature-responsive solenoid or other on/off type of control valve and through a microvalve or other micro-electric mechanical system to the consuming device. The solenoid valve can be selectively actuated to operate in either (1) an opened condition that permits liquid refrigerant to flow from the source to the microvalve or (2) a closed condition to prevent liquid refrigerant from flowing from the source to the microvalve. The microvalve, on the other hand, can be operated to modulate or otherwise control the amount of liquid refrigerant flowing therethrough to the consuming device. Thereafter, liquid refrigerant flows from the consuming device through a superheat or similar electronic controller back to the source of liquid refrigerant.
In normal operation of the refrigerant cooling system, when the sensed temperature of the device to be cooled (as determined by a temperature sensor) increases above a predetermined target temperature, the solenoid valve is caused to be opened. As a result, liquid refrigerant is allowed to flow through the solenoid valve from the source to the microvalve. The microvalve is, in turn, operated by the superheat or similar electronic controller to modulate or otherwise control the flow of liquid refrigerant therethrough to the consuming device as needed.
Subsequently, when the sensed temperature of the device to be cooled decreases below the predetermined target temperature, it is desirable to cease the flow of liquid refrigerant from the source to the consuming device. To accomplish this, the solenoid valve is initially closed. When this occurs, all of the remaining fluid contained within the microvalve is drawn out of the microvalve into the consuming device. As a result, the pressure of the fluid contained in the line downstream of the solenoid valve (as measured by a fluid pressure sensor that is typically provided as part of the superheat or similar electronic controller) drops to near zero. When this close-to-zero pressure situation occurs, the microvalve is then operated by the superheat or similar electronic controller to a fully closed condition.
Thereafter, when the sensed temperature of the case of the device to be cooled increases above the predetermined target temperature, the solenoid valve is caused to be re-opened to permit the flow of the liquid refrigerant from the source into the microvalve. However, because the fluid pressure sensor is located downstream of the microvalve as part of the superheat or similar electronic controller, the rise in the fluid pressure at the microvalve cannot be detected instantaneously by the superheat or similar electronic controller, which would preferably respond by opening or modulating the operation of the microvalve very quickly after the solenoid valve is re-opened. Rather, initially after the solenoid valve is re-opened, only a small amount of the liquid refrigerant passes through the microvalve and the consuming device to the superheat or similar electronic controller. That small amount of the liquid refrigerant eventually is sensed by the fluid pressure sensor provided as part of the superheat or similar electronic controller, which causes the microvalve to be re-opened.
Thus, it can be seen that there is an undesirably long period of time during which the pressure sensor continues to sense the close-to-zero pressure situation and maintain the microvalve in a closed condition, even after the solenoid valve has been re-opened to permit flow of the liquid refrigerant from the source into the microvalve. As a result, an undesirably long period of time occurs before the pressurized fluid is supplied in a sufficient quantity through the microvalve to the consuming device, thereby allowing cooling of the device to be cooled. Thus, it would be desirable to provide an improved system that avoids this problem.